The photochemical activity of native Central Siberian Scots pine trees (Pinus sylvestris L) was estimated from the middle of February to the middle of March 2001. We measured chlorophyll (Chl) fluorescence in attached intact needles from trees located approx. 30 km west of the Yenisey river (60°44'N, 89°09'E) near the village of Zotino. In this period, the air temperature varied between -39 °C and +7 °C. At temperatures below -10 °C, P. sylvestris needles did not exhibit any variable Chl fluorescence during the daylight period. During the night, however, the effective quantum yield of photosystem 2 (PS2) photochemistry, Φ2 [Φ2 = (Fm' - Ft)/Fm'), increased from values near zero to values between 0.05 and 0.20 depending on the needle temperature and sample investigated. The increase started soon after dusk and lasted for 3-6 h depending on the temperature. A faster increase of Φ2 was found for temperatures around -16 °C, and lower rates occurred at lower temperatures. Irrespective of the temperature, Φ2 decreased rapidly to near zero values at dawn, when the photosynthetic photon flux density increased to about 1-5 µmol m-2 s-1, and remained near zero throughout the day. At temperatures higher than -10 °C, the diurnal decrease and the nocturnal increase of Φ2 were less distinct or disappeared completely. Hence the winter-adapted Scots pine maintains some photochemical activity of PS2 even at extremely cold temperatures. The capacity of photochemical reactions below -10 °C is, however, very limited and PS2 photochemistry is saturated by an extremely low irradiance (less than 5 µmol m-2 s-1). and P. Šiffel, J. Šantrůček.
The responses of photosynthesis and growth to increasing CO2 concentration ([CO2]) were investigated in Hippophae gyantsensis and H. rhamnoides subsp. yunnanensis, which are endemic at the Qinghai-Tibet Plateau and phylogenetically related, but distributed parapatrically in divergent regions. Seedlings of the two species were grown at ambient [AC; 360 μmol(CO2) mol-1] and elevated [EC; 720 μmol(CO2) mol-1] [CO2] in growth chambers. The responses to EC were significantly different between the two species. EC induced an increase in photosynthesis, stomatal conductance, intrinsic water-use efficiency, apparent quantum efficiency, total dry mass, and a decrease in photorespiration rate, maximum carboxylation rate of Rubisco, and maximum electron transport rate in H. gyantsensis compared to those in H. rhamnoides subsp. yunnanensis. Moreover, a significant increase in leaf nitrogen content and a decrease in root/shoot ratio was also observed in H. gyantsensis. H. gyantsensis showed a significantly higher specific leaf area than that of H. rhamnoides through treatments. Relative to H. rhamnoides subsp. yunnanensis, H. gyantsensis showed a greater potential to increase photosynthesis and growth to cope with the increasing [CO2] and it might expand its distribution range in the future., F. Ma, T. T. Xu, M. F. Ji, C. M. Zhao., and Obsahuje seznam literatury
The article focuses on structural changes in the Bratislava population in the first half of the 20th century. Particularly in the decade of 1939–1948, there was an intense social engineering, i.e. a targeted effort to adjust both the ethnic and social city structures to the contemporary regime needs. The Czechs were the first target of these efforts (1939), followed by the Jewish minority (deportations in 1942); after the liberation, both Hungarian and German inhabitants fell victims to such activities, and after February 1948, this process also affected some social strata of the population. (A mass emigration after August 1968 was due to different reasons.) When analyzing the social engineering, the author has used particularly memories of the contemporary witnesses supported by the archive and other sources.